Conventional optical projection lithography has been the standard silicon patterning technology for the past 20 years. It is an economical process due to its inherently high throughput, thereby providing a desirable low cost per part or die produced. A considerable infrastructure (including steppers, photomasks, resists, metrology, etc.) has been built up around this technology.
In this process, a photomask, or “reticle”, includes a semiconductor circuit layout pattern typically formed of opaque chrome, on a transparent glass (typically SiO2) substrate. Each layer of the semiconductor circuit can be formed using one or more reticles, the arrangement and content of each reticle being configured and stored in a database. The content of the database is provided (e.g. “handed off”) to a fabrication site for fabrication of the semiconductor device according to the content of the database.
To improve the cycle time to get a new semiconductor device out of fabrication, a design team frequently breaks the database handoff into two parts. The first database part can include the drawn base layers and the second database part can include drawn programmation layers. Base layers are the layers needed to build Front End of Line (FEOL) reticles up through but not including a contact pattern (CONT). Programmation layers are the layers that define Back End of Line (BEOL) reticles (layers above CONT). This allows the reticle build and subsequent lead lot to begin before the entire database is handed off to the factory. The reason it is desired to hand off the final CONT drawn layer with the programmation patterns is that CONT is one of the drawn layers modified to finalize a database. CONT placements are modulated in Engineering Change Order (ECO) library macros to change the functionality and/or timing of logic designs. These ECO cells are generally the last cells to be finalized in a design. Up until the 90 nm flow, there was minimal interaction between the drawn layers that affected the build of FEOL versus BEOL reticles. It will be appreciated that the use of the CONT for ECO's is optional, and not mandatory. The present embodiments are directed to those situations where CONT is used for the ECO's.
However, beginning at 90 nm, the CONT drawn layer not only affects the CONT reticle, but it also strongly influences the Optical Proximity Correction (OPC) that needs to be applied to a polysilicon “POLY” layer reticle. Because the drawn POLY layer, which defines the GATE reticle, is handed off with the base layers and the final CONT pattern is handed off with the programmation layers, the POLY reticle cannot be manufactured until the programmation layers are handed off which is too late in the manufacturing flow.
Accordingly, a need exists to define a process and flow in a system which allows accommodation of layer dependencies without affecting the flow of mask build. The disclosure uses the example where the final CONT drawn level to be handed off with the programmation layers but include enough information about CONT in the base drawn layers to build reticles which are affected by the drawn CONT level.